The present invention relates to a thermo element suitable for use in an electronic control thermostat that performs control to vary the water temperature in an engine cooling water temperature control system that variably sets the cooling water temperature in accordance with the load of the internal combustion engine (called the xe2x80x98enginexe2x80x99 hereinafter) employed in an automobile or the like, for example.
Generally, a thermo element functions as an actuator that performs drive control of a thermostat valve or similar by causing a moving piston to advance toward and withdraw from the outside of a wax case in accordance with a change in the volume of thermo wax which is encapsulated in the case as a thermally expanding body. Further, as an example of a thermo element of this type, a thermo element is known which is constituted by providing, in or outside the case, heater means for performing control of the thermo wax temperature so as to permit control of the change in the volume of the thermo wax by means of heat which is generated by heater means.
As an example of a thermo element that comprises heater means of this type, a thermostat actuation member that comprises an electrical-resistance heating element, as illustrated by Japanese Patent Application Laid Open No. H8-222101, for example, is known. This conventional technology involves a wax-type thermal element structure in which an electrical-resistance heating element is disposed so as to be embedded in part of the wax encapsulated in the casing, and connecting wire material, which allows electricity to flow to the electrical-resistance heating element within the wax, is withdrawn in a hermetically sealed state via a harness withdrawal portion which is provided by encapsulating sealing material at an end of the casing.
However, in the case of the above-described conventional thermo element, because a resistive heating element is used as the heater means, not only is it difficult to set the heat generation temperature to a preset target temperature and to maintain and control this temperature, there have also been cases where a controller for performing control of the electrification of the resistive heating element must be provided outside the element and electrification control from the outside is necessary.
Furthermore, in the case of the above-described conventional thermo element, an element with a structure in which a heater made of metal foil is attached to a flat metal plate is employed as the electrical-resistance heating element and this element is simply embedded in the wax so as to face the wax. Because only the plate-shaped surface to which the metal foil of the metal plate is attached generates heat, although heat propagates to parts close to the heat-generating part of this surface, because the interval between the heat-generating part and the inner circumferential surface of the casing is not constant, the propagation of heat inside the casing is non-uniform, and the generation of a temperature variation was inevitable. There was therefore also the problem that it was difficult to efficiently raise the temperature of the whole of the wax encapsulated in the casing with this electrical-resistance heating element.
In addition, because two harnesses to which connecting wire material drawn from the heater means was soldered were withdrawn from a harness withdrawal portion that was formed by integrally molded sealing material, the sealing performance in this part was a problem and there was a risk of wax leaking to the outside as a result of the high pressures generated when the wax encapsulated in the casing expanded as a result of a rise in temperature.
The present invention was conceived in view of this matter, an object thereof being to provide a thermo element which not only permits the temperature of the whole of a thermally expanding body such as wax encapsulated in a case to be efficiently raised by means of heater means, and in which element the structure of a terminal withdrawal portion for controlling the electrification of the heater means from the outside is simple and affords a reliable sealing state, but which also allows control of the electrification of the heater means to be dispensed with.
In order to achieve this object, the thermo element according to the present invention (the invention according to claim 1) is a thermo element equipped with a thermally expanding body which is encapsulated in a tube-type case and which serves to allow a moving piston to advance toward and withdraw from the outside of the case in accordance with a change in the volume of the thermally expanding body that accompanies a variation in the temperature thereof, and a heating element which is disposed in the case and thermally affects the thermally expanding body, characterized in that the heating element has a substantially tubular shape and is disposed so as to be embedded in the thermally expanding body in a substantially central position in the case; an electrode member, which is connected to an external power supply via a terminal withdrawal portion provided at the end of the case on the opposite side to the piston, is disposed on the inner circumferential side of the heating element; a plate spring member which also serves as a heat radiation fin for radiating heat to the thermally expanding body is disposed at the circumference of the heating element between this circumference and the inside wall portion of the case, the plate spring member having a larger surface area than the heating element.
The thermo element according to the present invention (the invention according to claim 2) is the thermo element according to claim 1, characterized in that the terminal withdrawal portion comprises: an insulating tube body which is held at an end of the case in a state where sealing material is interposed between the insulating tube body and the end of the case; and a terminal which is arranged penetratingly within the insulating tube body in a state where sealing material is interposed between the terminal and the insulating tube body, the terminal being electrically connected to an electrode member which is provided in the heating element.
The thermo element according to the present invention (the invention according to claim 3) is the thermo element according to claim 1 or 2, characterized in that the plate spring member consists of an electrically conductive material and functions as a second terminal that permits electrical conduction between the heating element and the case by contacting the outer circumference of the heating element and the inside wall portion of the case.
The thermo element according to the present invention (the invention according to claim 4) is the thermo element according to any one of claims 1 to 3, characterized in that the electrode member comprises an electrically conductive plate spring member; and spring elements that cause a pressure contact force to act on the inner circumference of the heating element are provided on the electrode member.
The thermo element according to the present invention (the invention according to claim 5) is the thermo element according to claim 1, characterized in that the terminal withdrawal portion comprises: an insulating tube body which is held at an end of the case in a state where sealing material is interposed between the insulating tube body and the end of the case; and first and second terminals which are arranged penetratingly within the insulating tube body in a state in which sealing material is interposed between each of these terminals and the insulating tube body, the first terminal being electrically connected to an electrode member which is disposed on the inner circumferential side of the heating element, and the second terminal being electrically connected to at least either the plate spring member disposed on the outer circumferential side of the heating element or the outer circumferential side of the heating element.
The thermo element according to the present invention (the invention according to claim 6) is the thermo element according to claim 5, characterized in that insulating material is attached to that part of the plate spring member which makes contact with the inside wall portion of the case, this insulating material providing insulation between the plate spring member and the case.
The thermo element according to the present invention (the invention according to claim 7) is the thermo element according to any one of claims 1 to 6, characterized in that the heating element is constituted as a PTC thermistor equipped with a self-acting temperature control function.
The thermo element according to the present invention (the invention according to claim 8) is a thermo element equipped with a thermally expanding body which is encapsulated in a tube-type case and which serves to allow a moving piston to advance toward and withdraw from the outside of the case in accordance with a change in the volume of the thermally expanding body that accompanies a variation in the temperature thereof, and a heating element which is disposed in the case and thermally affects the thermally expanding body, characterized in that the heating element is substantially plate-shaped and is disposed so as to be embedded in the thermally expanding body in a substantially central position in the case; an electrode member, which is connected to an external power supply via a terminal withdrawal portion provided at the end of the case on the opposite side to the piston, is disposed on one side of the plate-shaped surface of the heating element; a plate spring member which also serves as a heat radiation fin for radiating heat to the thermally expanding body is disposed on the other side of the plate-shaped surface of the heating element between same and the inside wall portion of the case, the plate spring member having a larger surface area than the heating element.
The thermo element according to the present invention (the invention according to claim 9) is the thermo element according to claim 8, characterized in that the terminal withdrawal portion comprises: an insulating tube body which is held at an end of the case in a state where sealing material is interposed between the insulating tube body and the end of the case; and a terminal which is arranged penetratingly within the insulating tube body in a state where sealing material is interposed between the terminal and the insulating tube body, the terminal being electrically connected to an electrode member which is provided on one side of the plate-shaped surface of the heating element.
The thermo element according to the present invention (the invention according to claim 10) is the thermo element according to claim 8 or 9, characterized in that the plate spring member consists of an electrically conductive material and functions as a second terminal that causes electrical conduction between the other side of the plate-shaped surface of the heating element and the inside wall portion of the case by contacting the other side of the plate-shaped surface of the heating element and the inside wall portion of the case.
The thermo element according to the present invention (the invention according to claim 11) is the thermo element according to any one of claims 8 to 10, characterized in that a second plate spring member which comprises a heat radiation fin for radiating heat to the thermally expanding body is disposed between the electrode member which is disposed on one side of the plate-shaped surface of the heating element and the inside wall portion of the case; and insulating material is attached to that part of the second plate spring member which contacts the side of the electrode member or the inside wall portion of the case.
The thermo element according to the present invention (the invention according to claim 12) is the thermo element according to any one of claims 8 to 11, characterized in that the plate-shaped heating element is disposed in a position that is shifted from a central position in the case in a direction orthgonal to the plate-shaped surface; and an electrode member is disposed on the side of the heating element which is close to the inside wall portion of the case, and the plate spring member is disposed on the opposite side of the heating element.
The thermo element according to the present invention (the invention according to claim 13) is the thermo element according to any one of claims 8 to 12, characterized in that the electrode member comprises an electrically conductive plate spring member; and spring elements that cause a pressure contact force to act on the inner circumference of the heating element are provided on the electrode member.
The thermo element according to the present invention (the invention according to claim 14) is the thermo element according to claim 8, characterized in that the terminal withdrawal portion comprises: an insulating tube body which is held at an end of the case in a state where sealing material is interposed between the insulating tube body and the end of the case; and first and second terminals which are arranged penetratingly within the insulating tube body in a state in which sealing material is interposed between each of these terminals and the insulating tube body, the first terminal being electrically connected to an electrode member which is provided on one side of the plate-shaped surface of the heating element, and the second terminal being electrically connected to either the plate spring member or the other side of the plate-shaped surface of the heating element.
The thermo element according to the present invention (the invention according to claim 15) is the thermo element according to claim 14, characterized in that insulating material is attached to that part of the plate spring member which makes contact with the case, this insulating material providing insulation between the plate spring member and the case.
The thermo element according to the present invention (the invention according to claim 16) is the thermo element according to claim 8, characterized in that: a second electrode member is disposed so as to be interposed between the other side of the plate-shaped surface of the plate-shaped heating element and the plate spring member; and the terminal withdrawal portion comprises: an insulating tube body which is held at an end of the case in a state where sealing material is interposed between the insulating tube body and the end of the case; and first and second terminals which are arranged penetratingly within the insulating tube body in a state in which sealing material is interposed between each of these terminals and the insulating tube body, the first terminal being electrically connected to an electrode member which is provided on one side of the heating element, and the second terminal being electrically connected to the second electrode member.
The thermo element according to the present invention (the invention according to claim 17) is the thermo element according to claim 16, characterized in that insulating material is attached to that part of the plate spring member which makes contact with the inside wall portion of the case, this insulating material providing insulation between the plate spring member and the inside wall portion of the case.
The thermo element according to the present invention (the invention according to claim 18) is the thermo element according to any one of claims 8 to 17, characterized in that the heating element is constituted as a PTC thermistor equipped with a self-acting temperature control function.
According to the present invention, because a tubular or plate-shaped heating element (which may be a resistive heating element or a PTC thermistor) which is embedded in the thermally expanding body in the case is held by a plate spring member that serves as both a heat radiation fin and an electrode, the heat generated by the heating element can be efficiently and rapidly transmitted to the thermally expanding body. Therefore, when the thermo element is employed in the water temperature variable control of an electronically controlled thermostat, for example, the desired thermo element effects can be exhibited.
Further, according to the present invention, when a cylindrical heating element is used, because the surface area of the element itself is then large, the transmission of heat to the thermally expanding body can be executed even more rapidly and reliably.
In addition, in the case of a bipolar-type structure, by attaching insulating material to that part of the plate spring member that contacts the inside wall portion of the case, an insulation effect between the plate spring member and the case can be ensured, and by allowing the outside of the plate spring member to contact the case, it is possible to prevent damage resulting from pressurization during the thermal expansion of the thermally expanding body.
Furthermore, according to the present invention, because the heating element is held within the case as a result of being held between the electrode member and the plate spring member, even if the heating element is a PTC thermistor consisting of a ceramic material, damage such as cracking does not occur and reliability and durability are improved.
Moreover, according to the present invention, in the case of a monopolar structure, the overall structure is simplified because withdrawal is via the electrode member provided in the center of the case, and then the terminal withdrawal portion at the end of the case, and the terminal, while the plate spring member serves as a terminal such that electrification takes place via the case. Further, in so doing, a space for providing adequate sealing material can be secured in the terminal withdrawal portion, whereby reliability with respect to leakage and so forth of the thermally expanding body is improved.
Moreover, according to the present invention, by using a PTC thermistor as the heating element and providing same with a self-acting temperature control function, electrification control by an external controller is rendered unnecessary and it is possible to obtain a thermo element with the desired operational performance.